Many examples of sandals can be purchased widely at major suppliers and outlets. In addition to standard foam rubber sandals that appear to be most common, there are other specialty sandals that serve various niche markets. Massage sandals feature raised embossments on the insole that attempt to simulate a massaging action while walking. Birkenstock sandals have specially textured surfaces made of cork or rubber that gradually mold to the shape of the user's foot after extended walking.
Sandals, or forms of open footwear, are typically worn either in casual/informal situations, and/or ones that involve some degree of water exposure to the foot. It is common that cost-effective, water-resistant materials are used partially/wholly in the sandal construction, such as ethyl-vinyl acetate (EVA), polyurethane (PU), poly-ethylene (PE), poly-vinyl chloride (PVC), thermo-plastic rubbers (TPR) or pure rubber, as well as combinations of these polymers. In no instance is the combination of a rigid, porous material, effecting both a drying and massaging function, and a non-rigid material that comprise the remainder of the open footwear, taught.
There exists some related prior art along these lines:
EP0685257B1 (priority date May 26, 1995) describes shoe insoles that include a moisture absorbent material, and more particularly to a shoe insole of the type comprising at least two interconnected layers of material, of which at least one layer is moisture permeable and one layer defines at least one space filled with the moisture absorbent material. WO95/33555 (priority date May 26, 1995), and related cases, describe moisture absorbent material comprising a porous matrix of adsorbent material, with the pores containing a crystalline deliquescent compound. WO97145206 (priority date May 30, 1996), and related cases, describe an open cell polyurethane, non-swelling foam impregnated or coated into a non-woven fabric, comprising super absorbent ingredient particles. The disclosed material is a super absorbent, fluid locking, moldable footwear product that takes body fluids away from the surface, and gels or locks the fluids in place even while under pressure. The material is breathable and releases fluids through evaporation. US20080120869 (priority date Nov. 26, 2006) describes a footwear cover that has an inner-surface comprised of a water absorbent material. The moisture absorbent material is generally comprised of desiccating salt and/or metal oxide powders. References therein describe the general incorporation of porous, granular material into the matrix of the insole. EP2095733A1 (priority date Jul. 6, 2007) describes an absorbent insole which has the dual function of being absorbent and transpire-able while simultaneously providing a shock absorbent function. The resulting insole is realized in multiple, continuous layers (up to 5 discrete layers) the first layer being water repellant and subsequent layers being water absorbent by being comprised of hydrophilic, micro-porous materials. The main intention is to direct moisture from the foot continuously downward to the base layer, where it is presumably stored for re-evaporation when the footwear is not in use. EP2167725B1 (priority date Jul. 17, 2007) describes having a liquid-repelling and vapor permeable polymeric coating, obtained by a plasma treatment process, provided over the entire item of footwear and combined with a liquid-absorbing foot supporting foot-bed. U.S. Pat. No. 7,055,265 (priority date Aug. 29, 2002) describes a sandal system that has inter-changeable insoles that may be tailored to specific activities and exhibit different properties. U.S. Pat. No. 7,866,062 (priority date Oct. 13, 2004) describes a sandal wherein an insert-able body, amenable to absorbing impact, is designed to insert into a cavity in the main body of the sandal, U.S. Pat. No. 8,151,487 (priority date Jun. 2, 2005) describes a liner for footwear that is designed to absorb and dissipate moisture, comprising a moisture absorbing material with certain frictional characteristics that extends beyond the foot, and an adhesive layer designed to adhere the assembly to the footwear. None of the previous art describes a sandal that is partially or wholly comprised of a rigid porous material, such as sandstone. It is the focus of this application to describe a sandal whose contact surface with the foot is preferentially comprised partially or wholly of a rigid, porous material.